1. Field of the Invention
The present invention relates to a torsion beam axle suspension, and more particularly to a torsion beam axle suspension, in which a three-dimensional slant angle is given to mounts formed on one end of each of trailing arms.
2. Description of the Related Art
In general, a suspension in the vehicle is the apparatus, which is provided between a body and a wheel, for absorbing vibration or shock transmitted from a road surface during traveling to enhance stability such as turning stability, through connection of two linkages with one or multiple control arms, supporting by a spring and a shock absorber in upward and downward directions, and proper harmonization with high rigidity, flexibility, relative motion between the body and the wheel the other directions. Such a suspension is classified into a rigid axle suspension and an independent suspension in structure. The rigid axle suspension is employed to an rear axle for big vehicles such as buses, trucks and an rear axle for cars, while the independent suspension is to enhance a vehicle ride and stability by division of the axle and independent motion between both wheels, and is mainly employed to passenger cars.
The independent suspension includes a rear suspension, so-called a torsion beam axle suspension, which has a structure connecting right and left trailing arms to a torsion beam, and also has three types according to a position of attaching the torsion beam, such as an axle beam type (V-shape), a pivot axle type (reversed V-shape) and a coupled beam type (H-shape).
Such a torsion beam axle suspension is disclosed in U.S. Pat. No. 4,834,416.
FIG. 1 is a plan view illustrating a conventional torsion beam axle suspension, and FIG. 2 shows a state in which a transverse force is applied to the wheels of FIG. 1.
As shown in FIGS. 1 and 2, in a rear suspension of the vehicle comprising right and left trailing arms 1a and 1b respectively pivoted at the front ends for vertical swinging motion by way of bushings 2a and 2b, and a torsion beam 6 connecting the trailing arms 1a and 1b, the trailing arms 1a and 1b have swinging axes 7a and 7b inclined to intersect on the front side of the line joining the bushings 2a and 2b, and the bushings 2a and 2b are set to be nonlinear in such a manner that their elastic characteristics are different in small and large displacement ranges in relation to the direction perpendicular to the swinging axes 7a and 7b within the horizontal plane including the swinging axes of the trailing arms 1a and 1b 
In this manner, after angles of mounting brackets 3a and 3b are inclined on a plane, circumferential holes are formed in the bushings, and a resin plate is press-fitted into the holes. As a result, the bushings have nonlinear elastic characteristics. Thereby, a toe-in is realized with respect to a weak transverse force, and a toe-out is realized with respect to a strong transverse force. Unlikely, the toe-out is realized with respect to a weak transverse force, and a toe-in is realized with respect to a strong transverse force.
However, the torsion beam axle suspension has the following problems.
In the case where the toe-out is realized with respect to a turning outer wheel of the rear suspension during soft or hard cornering, there appears a tendency toward an over steer (O/S).
When this over steer appears strongly, this gives rise to a strong spin phenomenon. As a result, the vehicle is decreased in stability.
Further, by forming circumferential holes in the mounting bushings, or press-fitting the resin plate into the formed holes, the bushings have nonlinear elastic characteristics. Thus, the mounting parts have a reduced transverse rigidity.
Therefore, in order to secure continuous stability of the vehicle, it is necessary to maintain a linear toe-in relative to the transverse force as well as to secure sufficient transverse rigidity.